1. Field of the Invention
This invention relates to a xenon discharge lamp lighting device, more specifically a xenon discharge lamp lighting device for lighting a xenon discharge lamp used as a light source for projection type image devices such as direct reflection projection digital projectors, polarized reflection projection digital projectors, etc.
2. Description of the Related Art
The picture projection light source for an image projection device (projector) is used, for example, in movie theaters. This device conventionally uses a large xenon discharge lamp. The main lighting device used for lighting the xenon discharge lamp is a constant current control model that controls the input current such that the value is constant.
In a constant current control lighting device, a stable start for a xenon discharge lamp nearing the end of its lamp life requires a stronger current than the rated drive current to be supplied to the xenon discharge lamp. For this reason, a large model is used for the xenon discharge lamp lighting device, with high maximum input power and capable of supplying a strong current.
Meanwhile, in recent years, direct reflection or polarized reflection projection digital projectors have been developed as small image projection devices. The light source used in these projection digital projectors is a xenon discharge lamp with a high charged pressure of xenon gas, such as a xenon discharge lamp for which the xenon gas charged pressure upon lighting is at least 1.5 times that of a xenon discharge lamp used in a large image projection device.
Because this type of image projection device can be easily installed in a small space, it is well suited as an image projection device to be used in exhibit halls and other locations.
Thus, when actually using a small image projection device such as a projection digital projector in an exhibit hall or other location, there is a demand from a space-saving standpoint for a small lighting device for lighting the xenon discharge lamp, which is the light source for the image projection device. Also, exhibit halls have often already allocated the power available for use in each booth. Therefore, instead of a large model current-controlled lighting device with high maximum input power, a small model constant power-controlled lighting device is used, controlling the input current such that the input power value is constant.
However, when using a constant-power controlled lighting device for lighting a xenon discharge lamp in a projecting digital projector, a lighting failure can easily occur when starting the lamp, and lamp lighting failures occur frequently at startup, particularly in a xenon discharge lamp nearing the end of its useful life. Possible causes of such lamp lighting failure occurrences are as follows. FIG. 4 indicates changes in input power, input current, and lamp voltage immediately after starting a lamp. A lighting failure occurs after starting a xenon discharge lamp using a conventional constant power-controlled lighting device.
In FIG. 4, the left vertical solid line t1 indicates a point in time prior to starting a xenon discharge lamp. At the point in time indicated by this solid line t1, both the lamp input power and lamp current are 0. As for the lamp voltage, for a xenon discharge lamp with a rated drive lamp voltage of around 25V, for example, a no-load voltage of about 130V is applied.
Also, the left vertical dotted line t2 indicates the startup of a lighting igniter. With the startup of the lighting igniter, a dielectric breakdown occurs between the electrodes of the xenon discharge lamp, followed by a rush current. The rush current supply time period To is a minimum of 400 microseconds, and no special electrical control can be made during this supply time period.
The right vertical dotted line t3 is the ending time for the rush current supply time period, as well as the point where electrical control begins for lighting the xenon discharge lamp. Conventionally, constant power control begins at the point in time indicated by this dotted line t3.
As based on FIG. 4, immediately after the lamp startup, the thermionic discharge from the electrodes is insufficient, making the arc formed between the electrodes unstable. In addition, convection of xenon gas scaled with a high charging pressure causes the arc to waver, which further destabilizes the arc and lengthens the discharge distance, thus increasing the lamp voltage as shown by label (a). And in a constant power-controlled lighting device, the input current is controlled downward when the lamp voltage increases, as indicated by label (b), thus further destabilizing the arc. As a result, the lamp voltage increases further as shown with label (c), and the input current is controlled downward again as shown with label (d). Repeating this bad cycle results in the xenon discharge lamp light going out before a stable arc is formed.
The present invention is based on the circumstances described above, and proposes to provide, as a lighting device for lighting a xenon discharge lamp used in a projecting image device, a xenon discharge lamp lighting device that has few or no lighting failures upon starting the lamp, even when lighting it near the end of its useful life, and which is also small with a low maximum input voltage.
The xenon discharge lamp lighting device in the present invention is characterized by, in a lighting device for lighting a xenon discharge lamp used in a projecting image device, when lamp voltage increases between the ending point of the rush current supply time period, occurring upon starting a xenon discharge lamp lighting igniter, until a preset specified time period T has passed, increasing the input voltage in accordance with said lamp voltage increase amount, and thereafter providing constant current control.
In the xenon discharge lamp lighting device of the present invention, from the ending point of the rush current supply period, which occurs upon startup of the igniter for lighting the xenon discharge lamp, until a specified time T has passed, it is preferable for the input current to be controlled to 80-150% of the input current during rated drive.
Also, in the xenon discharge lamp lighting device of the present invention, it is preferable for the preset specified time T to be 50 milliseconds or more.
Using the composition above, after the xenon discharge lamp is started and immediately after the rush current supply period is complete, the input power would be increased according to the lamp voltage increase amount in the xenon discharge lamp. Therefore, even if the lamp voltage increases due to a destabilized arc, the input current does not decrease in response.
This allows reliable stabilization of the arc, which prevents or controls the occurrence of lighting failures upon lamp startup even when lighting a xenon discharge lamp near the end of its useful life.
In addition, after specified time T passes after the completion of the rush current supply time period occurring after starting the xenon discharge lamp, there is constant power control, making excessive input power unnecessary, which allows smaller maximum input power and decreased device size.